Spin noise spectroscopy (SNS), for the first time demonstrated on a sodium vapor [1]} back in 1981, has been rapidly developing over the past decade and has proven to be an efficient tool for studying the energy structure of matter (see, e. g., reviews [2]}, [3]}, [4]}, [5]}, [6]}).
To a large extent, the success of the SNS was inspired by its applicability for studies of semiconductor systems [7]}, [8]}, [9]}, [10]}, [11]}, including nanostructures [12]}, [13]}, [14]}. Not only spin carrier Larmor precession in volume ([9]}, [16]} etc.) and low-dimensional media (e. g. [17]}, [18]}) can be addressed by SNS, but also the nuclear dynamics [19]}, [20]}, [21]}, light-matter interaction effects [22]}, [23]}, spatial properties distribution [24]}, [25]}, and even noise of valley redistribution of electrons [26]}. Still the atomic systems attract the significant attention of researchers [27]}, [28]}, [29]}, [30]}, [31]}, [32]}, [33]}, [34]} as model objects which allow to reveal the fundamental pecularities of spin noise formation mechanics.
In typical SNS experiments with polarimetric detection of the signal, one measures, in fact, the magnetization-noise power spectrum of the studied sample associated, in accordance with the fluctuation-dissipation theorem, with the spectrum of its magnetic susceptibility [35]}.
The experiments are usually carried out in a transverse static magnetic field, so that the magnetization-noise power spectrum turns out to be localized in the region of the Larmor frequency \(\omega _L\) of precession of the magnetic moments (spins) and represents, in fact, EPR (electron paramagnetic resonance) spectrum of the system.
The fact that magnetization noise is observed in SNS as the polarization noise of the probe laser light and is caused by fluctuations of the optical susceptibility of the sample shows a similarity of the SNS and Raman spectroscopy.
Thus, due to combination of the features of the EPR and Raman spectroscopy, the SNS reveals a number of unique features related to nonperturbativity of the SNS [36]}, [37]}, to possibility of tuning the frequency of the probe laser light [38]}, [39]} and its spatial localization [40]}, to possibility of using multi-beam configurations [41]}, [42]} and some others.
